@Giorgio *****

Besides Hong Kong, at least one I know : Malaysia under MM2H program. Which at least gives some relevance to the OP's question...

@Richard ********

My original question was indeed about land crossing, but I am already aware that I also need something to show at my departure airport. I understand that buying one of these onward solutions is overkill for land crossings. At the contrary, some airports like HKG may be more demanding... these onward tickets are merely a reservation showing a PNR, but no confirmed e-ticket, right?

Thanks all for your for the insights from the field, I think I got a fine overview of the borders thing. I have been travelling for decades in SE, but since the covid interruption, I needed some update. Thank you.

@Myles ******

Well noted thanks.

@Myles ******

By air, it actually depends where from. I will fly from HKG where they are more likely to ask if I remember well and I will need something to show.